CHAPTER 2-1

ATOMS
• Atom – is the basic unit of matter
– Ex. Democritus – breaking a piece of chalk, when is it not chalk anymore? Until atomos “unable to be cut”
• An atom is very small. 100 million atoms make up about 1 cm.

ATOMS
• Atoms are made of smaller subatomic particles: protons, neutrons and electrons.
• Protons have a positive charge, neutrons a neutral charge and together they make up the nucleus of an atom
• Electrons are negatively charged and much smaller than protons
• Atoms have a neutral charge, equal number of electrons and protons

ELEMENT
• An element is a pure substance made up of just one type of atom
• Elements have a one or two letter symbol
• The number of protons equals the atomic number of the element

ELEMENT
• Atoms of the same element that differ in the number of neutrons they contain are known as isotopes.
– Isotopes are identified by their mass number
• Isotopes of an element are similar because they have the same number of electrons; all isotopes of an element have the same chemical properties.
• Radioactive isotopes are important to use for dating and labels to follow the movement of substances within organisms.

CHEMICAL COMPOUNDS
• A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions.
– Written in shorthand known as a chemical formula

CHEMICAL COMPOUNDS
• The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed.
– Ex. Sodium Chloride – Sodium and Chlorine

CHEMICAL BONDS
• The main types of chemical bonds are ionic bonds and covalent bonds.
• An ionic bond is formed when one or more electrons are transferred from one atom to another.
• Positively and negatively charge atoms are known as
ions.

CHEMICAL BONDS
• A covalent bond is formed when one or more pairs of electrons are shared between two atoms.
– Can be a single, double or triple bond

CHEMICAL BONDS
• A molecule is the smallest unit of most compounds.
– Ex. Water – H2O
– Doesn’t usually share electrons equally between the two atoms

CHEMICAL COMPOUNDS
• Van der Waals forces are a type of intermolecular interaction in which when molecules are close together, a slight attraction develops between the oppositely charge regions of nearby molecules.
– Ex. Tokay gecko